It is well known that thermal and photochemical yellowing are major concerns in magenta image stability of color prints. Over the years improvement in magenta image stability has been achieved by introducing more efficient image stabilizers. However, there still exists a need to further improve the resistance to yellowing in color paper.
It has been known for some time that compounds having the generic structure S are able to undergo reaction with residual magenta coupler and thereby effectively prevent both thermal and photochemical yellowing since the products of the reaction are not yellow and are not prone to yellowing. However, a major problem in the utilization of these compounds is the loss of coupler during storage of the photographic element prior to exposure and processing resulting in a reduction in color density in the print. See for example, U.S. Pat. No. 4,540,657 to Krishnamurthy and Japanese Patent Publication No. 62-31259 to Fuji Photo Film Co., Ltd. The generic structure of Compound S is represented below: ##STR3## wherein: A is a polyvalent atom, an acidic oxide group, a carboxylic group, a heterocyclic moiety, a carbocyclic group, or an alkane or substituted alkane group; each L is at least one divalent linking group; R.sub.1 and R.sub.2 are H, alkyl, cycloalkyl, aryl, heterocyclic, ester; n is a positive integer with a range of 1-6; m is a positive integer of at least one; with the proviso that at least one of A, L, R.sub. or R.sub.2 contains at least one ester or amide group derived from an acidic oxide of carbon, phosphorous, sulfur, boron or silicon.
In copending, commonly assigned application U.S. Ser. No. 08/000,431, filed Jan. 4, 1993, now U.S. Pat. No. 5,508,147, the disclosure of which is hereby incorporated by reference, we showed that the compound S-1 (having the structural formula set forth below) could be incorporated in a silver halide color photographic element containing a ballasted magenta coupler such that there is negligible loss of coupler prior to processing. This was achieved by coating the epoxy compound in separate layers that were adjacent to the imaging layer containing the magenta coupler and the green sensitized emulsion. Furthermore, it has also been demonstrated that mixing of S-1 with residual magenta coupler after processing may be achieved by using a pH dependent solubilizing agent, e.g., a fatty acid, such as myristic acid, in the coating and processing the coating using developer which preferably contains benzyl alcohol. However, the use of benzyl alcohol in the developer raises environmental concerns. ##STR4##
In an effort to eliminate the use of compounds such as benzyl alcohol to achieve post process mixing of the epoxy scavenger with the residual magenta coupler, copending, commonly assigned U.S. Ser. No. 08/255,512, filed Jun. 8, 1994, and now U.S. Pat. No. 5,543,276, the disclosure of which is hereby incorporated by reference, discloses novel terminal epoxy compounds containing a pH-dependent solubilizing moiety in the molecule. Dispersions of these compounds are coated in layers adjacent to the magenta imaging layer, and the compounds diffuse into the magenta layer upon processing where they react with residual magenta coupler yielding products that are not yellow or prone to yellowing. The approach is effective in reducing thermal and photochemical yellowing in processed prints without the use of benzyl alcohol.
The exemplified compounds disclosed in U.S. Ser. No. 08/255,512 now U.S. Pat. No. 5,543,276, are incorporated into photographic elements in the form of solid particle dispersions. It has been previously proposed in the photographic art to use solid particle dispersions as a means for incorporation of a variety of photographically useful compounds, for example, solid particle filter dye dispersions, as disclosed in, e.g., U.S. Pat. Nos. 4,294,916, 4,294,917, and U.S. Pat. No. 4,940,654. Techniques for making solid particle dispersions are very different from the techniques used to make conventional oil-in-water photographic dispersions. Typically, solid particle dispersions are made by mixing the solid of interest with an aqueous solution that may contain one or more grinding aids or stabilizers. Particle size reduction is accomplished by subjecting the solid crystals in the slurry to repeated collisions with hard, inorganic milling media, such as sand, spheres of silica, stainless steels silicon carbide, glass, zirconium, zirconium oxide, yttria-stabilized zirconium oxide, alumina, titanium etc., all of which fracture the crystals. The bead sizes typically range from 0.25 to 3.0 millimeters (mm) in diameter. Ball mills, media mills, attritor mills, jet mills, vibratory mills, etc. are frequently used to accomplish particle size reduction.
Problems have been identified, however, when photographic materials containing the epoxy compounds disclosed in U.S. Ser. No. 08/255,512 now U.S. Pat. No. 5,543,276, are stored at elevated temperatures (e.g., above about 45.degree. C.) prior to exposure and processing. Typically, it is found that there is significant loss in color density in the high exposure (or highlight) regions of the print if these materials are stored at elevated temperatures for long periods of time prior to exposure and processing. The latter is believed to result from unwanted migration of the epoxy compound from the adjacent nonimaging layer to the magenta imaging layer prior to processing. A method is therefore desired to improve the raw stock keeping properties of these materials at elevated temperatures.